Image quality setting preferred by the user for an image display apparatus varies depending on the ambient environment. Thus, there is an increasingly common technique in which an apparatus ascertains the ambient environment and performs image quality setting suitable for the environment for provision to the user. The apparatus can ascertain the ambient environment by various methods, e.g. by ascertaining the ambient brightness environment using an illuminance sensor, detecting movement of the viewer using an infrared sensor, or collecting ambient information by capturing an image of the surroundings by means of a video camera or the like, and analyzing the captured image.
One of the above-described methods adapted for many image display apparatuses uses a technique by which an ambient brightness environment is detected by an illuminance sensor and the display brightness is automatically adjusted to be suitable for viewing based on the detected brightness environment. For example, when the brightness environment is dark, it is possible to perform adjustment by reducing the screen brightness to the optimum brightness which does not dazzle the viewer. When, on the other hand, the screen brightness is insufficient in an extremely bright environment such as outdoors in fine weather (under direct sunlight), visibility becomes lower. The image quality adjustment based on the environment has been performed not only in the adjustment of the screen brightness, but also in various image quality settings such as contrast, black level, color density, and color temperature.
The image quality adjustment by an illuminance sensor is often used in a display apparatus used outdoors, such as a mobile phone, a public display (PD), a portable navigation device (PND), and an on-vehicle display, besides a display apparatus, such as a television, which is viewed indoors such as in an office or at home. Because brightness changes frequently outdoors, the image quality adjustment is frequently performed. Thus, natural image quality setting unlikely to discomfort the viewer, as well as application of the setting at a suitable timing is required.
A prior image display apparatus for performing image quality setting using an illuminance sensor is disclosed in Patent document 1. The display apparatus described in Patent document 1 sets the light-emission brightness and the timing for controlling brightness depending on the frequency of the change of the signal detected by an illuminance sensor. Patent document 2, for example, discloses another image display apparatus which performs brightness adjustment by using a plurality of illuminance sensors and calculating an average value, in an environment, such as outdoors, where brightness changes frequently.